Ink curing apparatus, comprising a housing containing a lamp partially surrounded by reflectors to direct UV radiation onto a substrate to cure ink, are well-known. Existing ink curing apparatus use reflectors to direct UV radiation from the lamp onto a substrate. The lamp is commonly surrounded by a moveable shutter. The shutter functions as a safety device, whereby when the apparatus is stopped and the power to the lamp is reduced the shutter is closed to shield the substrate from the heat of the lamp. When the power is reduced, any residual heat held in the lamp is retained within the apparatus, including being absorbed by the shutter. The shutter is opened to allow UV radiation to be directed through the opening between the reflectors, referred to as a “curing window”, onto the substrate.
Known shutter arrangements for UV curing apparatus include a single curved plate, or two complementary curved plates that meet each other when the shutter is in a closed position, to block radiation from the lamp reaching the substrate. The applicant's earlier UK Patent GB2495161 describes the use of such shutters in UV curing apparatus, wherein each of two shutters holds in place a reflector. Each shutter is moveable between an open position exposing the substrate to UV radiation and a closed position shielding the substrate from the UV lamp. Movement of the shutter/s in known devices is often generated by using an actuator, which is pneumatically or electrically powered; for example, shutter movement is controlled by a pneumatic drive having an actuator limited to a 180-degree field of movement. The pneumatic drive is used to move the two shutters together into a closed position and then apart into an open position. In alternative embodiments, an electric motor is used. Known drive means move in one direction to open the shutters and in the opposite direction to close the shutters. Thus, known devices only allow movement of the shutters between two discrete positions, whereby the curing window is either open or closed. The movement of the shutter is slow and, in some arrangements, it has been found that the shutter can effectively jolt between the two alternative positions. Furthermore, the stop-start movement of existing shutter mechanisms puts a significant amount of stress on the component parts of the apparatus.
Existing drive mechanisms are difficult to control to allow shutter movement with the desired accuracy and speed. The movement of a shutter/s having the above-described problems has been found to be particularly disadvantageous in the field of digital/inkjet UV print curing where the printing process is much quicker with the substrates for curing being moved rapidly through the UV curing apparatus. Slow and poorly-controlled shutter movement is a significant limitation to the speed and output volume of the digital print process.